1. Field of the invention
The present invention relates to gas sensor elements equipped with a solid electrolyte having proton conductivity and methods of detecting a concentration of a component contained in target detection gas by using a gas sensor element.
2. Description of the Related Art
Air pollution is the introduction of chemicals, particulate matter, or biological materials emitted from internal combustion engines for motor vehicles, etc., that causes harm or discomfort to humans or other living organisms, or causes damage to the natural environment or built environment, into the atmosphere. Pollution control standards acts and regulations on chemicals, particulate matter, or biological materials contained in exhaust gas emitted from internal combustion engines for motor vehicles become stricter year by year.
For example, there have been proposed various types of gas sensor elements and techniques which directly detect a concentration of a component contained in exhaust gas such as nitrogen oxide (NOx) gas, hydrogen gas, hydrocarbon, etc. and transmit detected data to an engine combustion control monitor, a catalyst monitor, etc. It is therefore necessary from the above views to provide a gas sensor element capable of detecting a concentration of hydrogen gas and hydrocarbon, etc. contained in exhaust gas as a target detection gas to be detected.
There is a conventional technique, disclosed in Japanese patent laid open publication No. JP 2003-185624, which provides a moisture tester capable of detecting a quantity of moisture contained in a target detection gas to be detected. However, the moisture tester does not detect a concentration of hydrogen gas or hydrocarbon gas. Such a conventional moisture tester has a solid layer of a proton conductive type installed between two positive electrodes and a negative electrode. The two positive electrodes are made of an electron conductivity material. A block layer is formed between one positive electrode and the solid layer. The block layer substantially blocks the proton conductivity between the positive electrode and the solid layer.
The conventional moisture tester disclosed in Japanese patent laid open publication No. JP 2003-185624 detects a first current in an electric circuit containing one positive electrode in which the block layer is formed and detects a second current flowing through an electric circuit containing the other positive electrode in which no block layer is formed. The moisture tester detects a current generated by the proton conductivity on the basis of a difference between the first current value and the second current value. The moisture tester can detect a content of water in the target detection gas to be detected with high accuracy.
A known conventional gas sensor element using the solid electrolyte having proton conductive type has the following drawback. A current generated by the proton conductivity flows in a solid electrolyte layer in a conventional gas sensor element in addition to a current generated by the electron conductivity. It is necessary for the conventional gas sensor element to detect a concentration of a target detection gas containing hydrogen atoms on the basis of a detected current value which corresponds to the sum of a current generated by the proton conductivity and a current generated by the electron conductivity. It is therefore difficult to detect the concentration of a target detection gas containing hydrogen atoms on the basis of the current sum of the proton conductivity and the electron conductivity with high accuracy.
The moisture tester disclosed in Japanese patent laid open publication No. JP 2003-185624 introduces proton through a side part of the positive electrode and the block layer. This decreases the detection accuracy when it detects hydrogen gas or hydrocarbon gas.